The present invention relates an intermediate-coating-less system (two-coat system) in which a top coating paint is directly coated on an electrodeposited coating, which is useful for paint industry, especially automobile coating. In detail, it relates a method for forming a plural layered electrodeposited coating and a method for forming a multi-layered coating containing this electrodeposited coating, which has excellent appearance, solvent resistance, weather resistance and corrosion resistance equal to a three layer coating by pigment alignment and which has a important roll on structuring a novel coating system which accomplishes decreasing coating step, reducing cost and decreasing damage to environment.
Lately, in paint field, especially in the field of automobile coating, decreasing coating step is strongly required in order to solve the problems of resource saving, cost-saving and decreasing damage to environment (VOC and HAPs, etc.). Specifically, there is desired a method for forming a coated film that, when compared with three layer coating having an electrodeposited primer coating, an intermediate coating and a top coating which are a conventional coating and finish procedures of automobile, the intermediate-coating-less ( two-coat system) in which top coating is carried out directly on an electrodeposited primer coating decreases number of coating steps, and keeps excellent appearance, cohesiveness to top coating, weather resistance and corrosion resistance equal to the three layer coating.
Regarding plural layered electrodeposited coating by way of the intermediate-coating-less system, Japanese Patent Publication No. 2-33069 discloses an electrocoating composition which forms two-layered coating having thick film. This invention is directed to a composition wherein a cationic acryl resin having a softening point of 80xc2x0 C. or more and a cationic phenol type epoxy resin having a softening point of 75xc2x0 C. or less are contained at a ratio of 1 to 30:1 by weight. It is described that the coated film formed from this composition has a two layer structure composed of an epoxy type underlayer having good corrosion resistance and an acryl type upper layer having good weather resistance.
Japanese Patent Publication No. 6-99652 also discloses that a two layered electrodeposited coating can be formed from an epoxy type cation electrodepositable resin and a non-ionic film-forming resin, which have a surface tension of a given region
In addition, Japanese Laid-Open Patent Application Nos. 8-333528 and 10-292131 disclose that a two layered electrodeposited coating can be formed from an amine modified epoxy type cation resin, a (self-crosslinking) acryl type cationic resin which has lower solubility parameter than the former resin, and a block polyisocyanate curing agent.
The above invention of each reference merely shows a means for separating resins in an electrodeposited coating, but does not describe the means for providing an electrodeposited coating having excellent appearance and excellent cohesiveness to a top coating, equal to the three layer coating.
An object of the present invention is to provide a coating method of intermediate-coating-less, which sufficiently keeps excellent appearance, weather resistance and corrosion resistance equal to a three layer coating in conventional technology.